首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   64480篇
  免费   268篇
  国内免费   576篇
系统科学   1283篇
丛书文集   433篇
教育与普及   305篇
理论与方法论   551篇
现状及发展   34353篇
研究方法   1379篇
综合类   24823篇
自然研究   2197篇
  2013年   828篇
  2012年   839篇
  2011年   2945篇
  2010年   515篇
  2009年   632篇
  2008年   1080篇
  2007年   1232篇
  2006年   1286篇
  2005年   1482篇
  2004年   2590篇
  2003年   2183篇
  2002年   1920篇
  2001年   1648篇
  2000年   1161篇
  1999年   1120篇
  1998年   648篇
  1997年   779篇
  1996年   543篇
  1994年   692篇
  1993年   691篇
  1992年   1045篇
  1991年   894篇
  1990年   964篇
  1989年   774篇
  1988年   753篇
  1987年   782篇
  1986年   820篇
  1985年   986篇
  1984年   853篇
  1983年   752篇
  1982年   858篇
  1981年   886篇
  1980年   1000篇
  1979年   1641篇
  1978年   1431篇
  1977年   1447篇
  1976年   1212篇
  1975年   1234篇
  1974年   1215篇
  1973年   1408篇
  1972年   1495篇
  1971年   1590篇
  1970年   1750篇
  1969年   1510篇
  1968年   1409篇
  1967年   1349篇
  1966年   1140篇
  1965年   874篇
  1958年   728篇
  1957年   581篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
Summary Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics.  相似文献   
172.
翟展胜 《太原科技》2003,(2):62-62,64
通过分析影响光缆接续质量的因素,从减少本征影响、克服技术因素、优化综合处置、减弱和避开环境影响4方面针对性地提出了实际施工中应采取的施工方法,以控制和减小不利影响,提高光缆工程的接续质量,为建设高质量传输线路提供有力保证。  相似文献   
173.
174.
The genetic engineering of production traits in domestic animals   总被引:1,自引:0,他引:1  
  相似文献   
175.
报道一种新颖的激光开槽、埋槽电极硅太阳电池的结构、工艺流程及其研制结果。在AM1.5,25℃,100mW/cm2的条件下,以面积为45cm3的36片硅片研制的硅太阳电池的输出参数的平均值为JSC=36.1mA/cm2,V∞=633mV,F.F.=0.798,η=18.23%,最后分析了种高性能硅太阳电池的设计特点。  相似文献   
176.
Abstract: After a recursive multi-step-ahead predictor for nonlinear systems based on local recurrent neural networks isintroduced, an intelligent PID controller is adopted to correct the errors including identified model errors and accumulatederrors produced in the recursive process. Characterized by predictive control, this method can achieve a good controlaccuracy and has good robustness. A simulation study shows that this control algorithm is very effective.  相似文献   
177.
Dynamic Characteristics of Inter-Satellite Links in LEO Networks   总被引:1,自引:0,他引:1  
To establish an efficient inter-satellite link (ISL) in an LEO network, the effect of geometric characteristics of ISL on the ISLs and the devices on the LEO satellite should be examined. Because of the continuous movement of the LEO satellite, the time-varying behaviours of the ISL's geometric charactersistics continuously change with the changes of the satellite's position on the orbit. These dynamic geometric characteristics of the ISLs are important for ISL's performance analyzing and the design of the devices on the LEO satellite. This paper describes dynamic geometric characteristics of ISL, analyzes the impact of these regulations on the tracking system of the satellite's antenna and the power adjusting system of the satellite's transmitter, with the Iridium system as an example.  相似文献   
178.
With time-based competition and rapid technology advancements, effective manufacturingscheduling and supply chain coordination are critical to quickly respond to changing marketconditions. These problems, however, are difficult in view of inherent complexity and variousuncertainties involved. Based on a series of results by the authors, decomposition and coordination byusing Lagrangian relaxation is identified in this paper as an effective way to control complexity anduncertainty.A manufacturing scheduling problem is first formulated within the job shop context withuncertain order arrivals, processing times, due dates, and part priorities as a separable optimizationproblem. A solution methodology that combines Lagrangian relaxation, stochastic dynamicprogramming, and heuristics is developed. Method improvements to effectively solve large problemsare also highlighted. To extend manufacturing scheduling within a factory to coordinate autonomicmembers across chains of suppliers, a decentralized supply chai  相似文献   
179.
It has long been realized that the problem of radar imaging is a special case of image reconstruction in which the data are incomplete and noisy. In other fields, iterative reconstruction algorithms have been used successfully to improve the image quality. This paper studies the application of iterative algorithms in radar imaging. A discrete model is first derived, and the iterative algorithms are then adapted to radar imaging. Although such algorithms are usually time consuming, this paper shows that, if the algorithms are appropriately simplified, it is possible to realize them even in real time. The efficiency of iterative algorithms is shown through computer simulations.  相似文献   
180.
Summary A new bromotyrosine-derived alkaloid with antileukemic activity, purealidin A (5), has been isolated from the Okinawan marine spongePsammaplysilla purea and its chemical structure elucidated on the basis of the spectroscopic data.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号